System and method for transmitting ancillary data

ABSTRACT

A method and system for encoding ancillary information at a transmitter in a high-speed communications network, the method comprising: generating an electromagnetic interference (EMI) reduction signal; receiving an ancillary data symbol; generating an EMI reduction signal variation based on the ancillary data symbol; and varying a characteristic of the EMI reduction signal based on the generated EMI reduction signal variation to encode the ancillary data symbol in the varied EMI reduction signal.

FIELD

The present disclosure relates generally to the field of datacommunications.

BACKGROUND

Some communications systems transmit ancillary data, which can servedifferent purposes, for example to send information about the status ofdifferent elements in the system or to allow changing configuration ofdevices that are remotely connected. Some systems have a high number ofinterconnections, so it is desirable not to add more channels, whichcould be difficult to route, and that would require supplemental pins onthe electronic devices.

Filters have been used in existing high-speed connections to carry extrainformation such as ancillary data on a separate channel or frequencyspectrum. These filters however do not perfectly eliminate thedeleterious effects of the ancillary data on the high-speed messagechannel, and reduce the performance of the latter due to informationleaking from the ancillary data channel into the high-speed messagechannel, the leaking information being perceived as noise in thehigh-speed message channel. Leakage from the message channel into theancillary data channel can also affect the performance of the ancillarydata channel.

A further disadvantage associated with the use of filters relates to thediscontinuities associated with the connection of the filters, and theimpedance of these circuits, which cause undesirable effects on thehigh-speed channel.

Transmitting ancillary data also usually requires additional transmitterand receiver circuits for transmission and decoding of the informationto be sent and received.

It is desirable to provide a data communications system that overcomesthese problems associated with the transmission of ancillary data.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graph showing an exemplary spread-spectrum clocking (SSC)profile.

FIG. 2 is a graph showing the frequency spectra of a signal having SSCand a signal without SSC.

FIG. 3 is a block diagram of an exemplary clock recovery circuit knownin the art.

FIG. 4 is a block diagram of an exemplary type-II clock recovery circuitknown in the art.

FIG. 5 is a block diagram of a communication system according to anembodiment of the present disclosure.

FIG. 6 is a flowchart of a method to encode ancillary data according toan embodiment of the present disclosure.

FIG. 7 is a flowchart of a method to decode ancillary data according toan embodiment of the present disclosure.

FIG. 8 is a graph showing an SSC profile variation encoding ancillarydata according to an embodiment of the present disclosure.

FIG. 9 is a graph showing an SSC profile variation encoding ancillarydata according to an embodiment of the present disclosure.

FIG. 10 is a graph showing an SSC profile variation encoding ancillarydata according to an embodiment of the present disclosure.

FIG. 11 is a graph showing the extraction of a received SSC symbol rateoffset according to an embodiment of the present disclosure.

FIG. 12 is a graph showing an SSC profile variation encoding ancillarydata according to an embodiment of the present disclosure.

FIG. 13 is a graph showing an SSC profile variation encoding ancillarydata according to an embodiment of the present disclosure.

FIG. 14 is a graph showing an SSC profile variation encoding ancillarydata according to an embodiment of the present disclosure.

FIG. 15 is a graph showing an SSC profile variation encoding ancillarydata according to an embodiment of the present disclosure.

FIG. 16 is a graph showing an SSC profile variation encoding ancillarydata according to an embodiment of the present disclosure.

FIG. 17 is a block diagram of a decoder according to an embodiment ofthe present disclosure.

FIG. 18 is a flowchart of an SSC decoding method for decoding ancillarydata from an SSC profile symbol according to an embodiment of thepresent disclosure.

DETAILED DESCRIPTION

The present disclosure provides, in an embodiment, a method for encodingancillary information at a transmitter in a high-speed communicationsnetwork, the method comprising: generating an electromagneticinterference (EMI) reduction signal; receiving an ancillary data symbol;generating an EMI reduction signal variation based on the ancillary datasymbol; and varying a characteristic of the obtained EMI reductionsignal based on the generated EMI reduction signal variation to encodethe ancillary data symbol in the varied EMI reduction signal.

In a further embodiment of the present disclosure, the EMI reductionsignal comprises a spread-spectrum clocking (SSC) profile, andgenerating the EMI reduction signal variation comprises generating anSSC profile variation; and varying the characteristic of the EMIreduction signal comprises varying the SSC profile according to the SSCprofile variation.

In a yet further embodiment of the present disclosure, varying the SSCprofile comprises mapping the received ancillary data symbol to apeak-to-peak amplitude variation of the SSC profile.

In a yet further embodiment of the present disclosure, the SSC profilevariation comprises a maximum peak amplitude, and a minimum peakamplitude having an equal magnitude and opposite polarity to the maximumpeak amplitude.

In a yet further embodiment of the present disclosure, the SSC profilevariation comprises a maximum peak amplitude, and a minimum peakamplitude having a different magnitude and opposite polarity to themaximum peak amplitude.

In a yet further embodiment of the present disclosure, varying the SSCprofile comprises mapping the received ancillary data symbol to a symbolduration variation of the SSC profile.

In a yet further embodiment of the present disclosure, the duration ofthe SSC profile variation is delineated by times when an instantaneoussymbol rate offset of the transmitter is equal to a nominal symbol rateof the transmitter.

In a yet further embodiment of the present disclosure, varying the SSCprofile comprises mapping the received ancillary data symbol to both apeak-to-peak amplitude variation and a symbol duration variation of theSSC profile.

In a yet further embodiment of the present disclosure, the duration ofthe SSC profile variation is delineated by times when an instantaneoussymbol rate offset of the transmitter is equal to a nominal symbol rateof the transmitter.

In a yet further embodiment of the present disclosure, the SSC profilevariation comprises a maximum peak amplitude, and a minimum peakamplitude having an equal magnitude and opposite polarity to the maximumpeak amplitude.

In a yet further embodiment of the present disclosure, the SSC profilevariation comprises a maximum peak amplitude, and a minimum peakamplitude having a different magnitude and opposite polarity to themaximum peak amplitude.

In a yet further embodiment of the present disclosure, the methodfurther comprises transmitting an EMI-reduced message signal at a symbolrate, the symbol rate specified by the EMI reduction signal.

In a yet further embodiment of the present disclosure, the methodfurther comprises: assessing the quality of the EMI-reduced messagesignal; and selecting an SSC profile to reach a target quality for theEMI-reduced message signal.

In a yet further embodiment of the present disclosure, the EMI-reducedmessage signal includes padding to adjust an average EMI-reduced messagesignal symbol rate to a target range.

In a yet further embodiment of the present disclosure, the symbol rateis substantially similar to a nominal symbol rate of the transmitter.

Another embodiment of the present disclosure provides a method fordecoding ancillary information at a receiver in a high-speedcommunications network, the method comprising: receiving an EMI-reducedmessage signal transmitted with an EMI reduction signal, the EMIreduction signal having an EMI reduction signal variation encoding anancillary data symbol; extracting the EMI reduction signal variation ata demodulator; and decoding the ancillary data symbol from the extractedEMI reduction signal variation at a decoder.

In a further embodiment of the present disclosure, the EMI reductionsignal comprises a spread-spectrum clocking (SSC) profile, and receivingthe EMI reduction signal comprises receiving an SSC profile; extractingthe EMI reduction signal variation comprises extracting an SSC profilevariation; and decoding comprises decoding the ancillary data symbolfrom the extracted SSC profile variation.

In a yet further embodiment of the present disclosure, decodingcomprises comparing the SSC profile variation to a mask corresponding tothe ancillary data symbol.

In a yet further embodiment of the present disclosure, decodingcomprises comparing a peak-to-peak amplitude of the SSC profilevariation to an expected peak-to-peak amplitude corresponding to theancillary data symbol.

In a yet further embodiment of the present disclosure, the methodfurther comprises: receiving a pilot symbol; and correcting theextracted SSC profile variation according to the pilot symbol.

In a yet further embodiment of the present disclosure, the methodfurther comprises correcting the extracted SSC profile variation by thedifference between the magnitude of the maximum peak and the magnitudeof the minimum peak of the extracted SSC profile variation, the expectedmagnitude of the maximum peak equal to the expected magnitude of theminimum peak.

In a yet further embodiment of the present disclosure, the methodfurther comprises correcting the extracted SSC profile variation by theaverage magnitude of the extracted SSC profile variation, the expectedaverage magnitude equal to zero.

In a yet further embodiment of the present disclosure, decodingcomprises comparing a peak-to-peak duration of the extracted SSC profilevariation to an expected peak-to-peak duration corresponding to theancillary data symbol.

In a yet further embodiment of the present disclosure, the methodfurther comprises: selecting an EMI reduction signal variation bincorresponding to the extracted EMI reduction signal variation, the EMIreduction signal bin being a nominal value mapped to a range of EMIreduction signal variation values; and decoding, at a decoder, theancillary data symbol from the selected EMI reduction signal variationbin.

In a yet further embodiment of the present disclosure, the range of EMIreductions signal variation values is at least twice the expectedmaximum constant difference between a received symbol rate and atransmitted symbol rate.

In a yet further embodiment of the present disclosure, the SSC profilehas a constant cycle duration, and the SSC profile comprises a pluralityof sections, the sum of the durations of all the SSC profile sectionsbeing equal to the constant cycle duration of the SSC profile.

Another embodiment of the present disclosure provides a transmitter fortransmitting ancillary information in a high-speed communicationsnetwork, the transmitter comprising: an input configured to receive amessage; an encoder configured to: obtain an electromagneticinterference (EMI) reduction signal; receive an ancillary data symbol;generate an EMI reduction signal variation based on the ancillary datasymbol; vary a characteristic of the obtained EMI reduction signal basedon the generated EMI reduction signal variation to encode the ancillarydata symbol in the varied EMI reduction signal; a modulator configuredto vary a symbol rate of the transmitter based on the varied EMIreduction signal; and an output configured to transmit the messageaccording to the varied symbol rate.

In a further embodiment of the present disclosure, the EMI reductionsignal comprises a spread-spectrum (SSC) profile, and the processor:generates an SSC profile variation; and varies the SSC profile accordingto the SSC profile variation.

In a yet further embodiment of the present disclosure, the transmitterfurther comprises a transmitter for transmitting an EMI-reduced messagesignal at a symbol rate, the symbol rate specified by the EMI reductionsignal.

In a yet further embodiment of the present disclosure, the processor:assesses the quality of the EMI-reduced message signal; and selects anSSC profile to reach a target quality for the EMI-reduced messagesignal.

Another embodiment of the present disclosure provides a receiver fordecoding ancillary information in a high-speed communications network,the receiver comprising: an input configured to receive an EMI-reducedmessage signal transmitted at a time-varying symbol rate, thetime-varying symbol rate based on an EMI reduction signal variationencoding an ancillary data symbol; a clock recovery circuit configuredto operate in a clock recovery mode to demodulate the time-varyingsymbol rate of the EMI-reduced message signal, and to operate in a dataextraction mode to extract the EMI reduction signal variation; and adecoder for decoding the ancillary data symbol from the extracted EMIreduction signal variation.

In a further embodiment of the present disclosure, the EMI reductionsignal comprises a spread-spectrum clocking (SSC) profile, and thedemodulator extracts an SSC profile variation; and the decoder decodesthe ancillary data symbol from the SSC profile variation.

In a yet further embodiment of the present disclosure, the clockrecovery circuit comprises: a phase error detector for comparing areceived symbol rate to a local reference clock signal and computing aphase error between the received symbol rate and the local referenceclock signal; an accumulator for summing phase errors; and a multiplierfor multiplying the output of the accumulator by a constant value toobtain an instantaneous symbol rate.

In a yet further embodiment of the present disclosure, the signs of thephase errors are used for the summation.

Reference to specific elements of various embodiments of the presentdisclosure will now be made.

FIG. 1 is a graph showing an exemplary spread-spectrum clocking (SSC)profile 100. SSC profile 100 shows the instantaneous message symbol rateoffset 101 of a message data signal relative to its nominal symbol rate102, expressed as a parts-per-million (ppm) ratio, over time. The term“SSC profile” will be used herein to refer to the characteristics of atransmitter's message symbol rate offset, relative to the transmitter'snominal symbol rate. The symbol rate of a message to be transmitted maybe expressed as a bit rate, representing the number of bits transmittedper second, or more generally as a symbol rate, measured in baud,representing the number of symbols transmitted per second. A symbol is amessage pattern representing an integer number of bits. Therefore,depending on the modulation scheme of a communications system, theinstantaneous and nominal symbol rates of the SSC scheme may refer to asymbol rate or to a bit rate. While a baud is a measure of symbol rate,the term “baud rate” is often used interchangeably with symbol rate. Thepresent disclosure uses baud rate and symbol rate interchangeably.

SSC is a means to reduce electromagnetic emissions (EMI) over a narrowfrequency band. These emissions are often subject to norms andregulations, for which SSC can be used to obtain compliance. Generally,SSC comprises a low-frequency variation of the average baud rate of atransmitter over time, which varies the instantaneous frequency of anundesirable EMI spur, lowering the peak radiation of the transmitter.

FIG. 2 is a graph 200 showing the effect of SSC in reducing an EMI spur.Spectral line 210 shows an exemplary EMI frequency spectrum of atransmitted signal without SSC. Because the transmit clock is a constantvalue, the transmitted signal produces a peak EMI spur 211 in spectrum210. Spectral line 220 shows an exemplary EMI frequency spectrum of asignal transmitted with SSC. Varying the transmit symbol rate averagesthe EMI power across the frequency spectrum and lowers the peak EMIvalue 221 of spectrum 220. The reduction in peak EMI is shown as thedifference between peak 211 and peak 221.

The SSC profiles used for EMI reduction are typically single-patternsymbol rate modulation profiles, whose modulation cycle duration,maximal symbol rate excursion, average symbol rate and maximal rate ofchange of the symbol rate are described by the given transmissionprotocol.

The symbol rate of a message transmitted with SSC has to be constantlymodified to provide measured EMI reduction. A repeating SSC profileprovides the necessary constant variations for EMI reduction.Furthermore, symbol rate variations of an SSC profile are bounded to asmall fraction of the nominal symbol rate (typically below +/−1%).

The variation of the message symbol rate over time imposes constraintson clock recovery circuits. Since the average symbol rate varies overtime, the clock recovery circuit is typically designed to tolerate thefull range of the message symbol rate.

FIG. 3 shows a clock recovery circuit 300 according to an embodiment ofthe present disclosure. Clock recovery circuit 300 contains a phaseerror detector 303 between the input data 301 and the reference clock302, and a feedback loop 304 that seeks to minimize this error. In aconventional communication system, a type-I feedback loop may besufficient when SSC is not enabled. Once settled, such systems willtrack limited static symbol rate offsets between the receiver and thetransmitter. However, when SSC is enabled, a type-II feedback loop istypically required.

FIG. 4 shows an exemplary type-II clock recovery circuit according to anembodiment of the present disclosure. Within selected high-speed symbolrate limits, type-II clock recovery circuit 400 can track a constantrate of change of the message symbol rate with a limited error.Transmission protocols that support SSC describe these requirements,which limit the amount of SSC-induced jitter on the recovered data.

Conventionally, ancillary data, which is data separate from messagedata, transmitted and received on a separate frequency channel, must bedecoded from the carrier by filters, which reduces the performance ofthe communications system and increases transmitter and receivercomplexity. Ancillary data can be referred to as low-speed data. Messagedata can be referred to as high-speed data.

In an embodiment of the present disclosure, the spread-spectrum clockingmechanism of a communications system is used to transmit ancillary data,in addition to providing EMI spur frequency dispersion for thehigh-speed transmission. The changes in instantaneous symbol rate overthe nominal symbol rate, that are a feature of conventional SSC and thatdescribe an SSC profile herein, are modulated in amplitude, frequency,shape, or a combination thereof, to carry the ancillary data signal froma high-speed transmitter to a high-speed receiver.

For transmission protocols that support SSC, the transmission of thissupplemental ancillary information can be made fully protocol-compliantby ensuring that the characteristics imposed on the SSC profile arerespected by the transmitter modulator. Advantageously, a receiveraccording to an embodiment of the present disclosure can decode theancillary data from the received signal without the need for theadditional filter circuits necessitated by a conventional separatefrequency channel ancillary data transmission scheme. By decodingancillary data through the use of the components of the type-II clockrecovery circuit typically present in SSC-compliant receivers,embodiments of the present disclosure make more efficient use ofreceiver circuit components.

FIG. 5 is a block diagram of a communication system 500 according to anembodiment of the present disclosure. An SSC profile encoder 502receives an ancillary data symbol 501 and generates an SSC profilevariation based on the ancillary data symbol 501. The encoder 502 variesat least one characteristic of an SSC profile based on the SSC profilevariation to encode the ancillary data symbol 501 in the varied SSCprofile. An SSC modulator 503 uses the time-varying SSC profile, whichincludes the encoded ancillary data symbol 501, to modulate the messagedata 504 at transmitter 505 for transmission. The transmitted messagesignal includes SSC to reduce peak EMI and also includes the encodedancillary data symbol. Receiver 510 receives the transmitted EMI-reducedmessage signal at a time-varying symbol rate. A clock recovery circuit511 operating in a clock recovery mode demodulates the time-varyingsymbol rate of the EMI-reduced signal in order to recover the nominalsymbol rate of the transmitter for deserializing the received messagedata 513. The clock recovery circuit 511 also operates in a dataextraction mode to extract the SSC profile variation from thetime-varying symbol rate. The SSC profile decoder 512 decodes theextracted SSC profile variation by demapping or comparing the extractedSSC profile variation to an expected SSC profile variation correspondingto an ancillary data symbol, thus recovering the transmitted ancillarydata 514.

FIG. 6 is a flowchart of a method 600 to encode ancillary data accordingto an embodiment of the present disclosure. At 601, an encoder generatesan electromagnetic interference (EMI) signal. At 602, the encoderreceives an ancillary data symbol. At 603, the encoder generates an EMIreduction signal variation based on the ancillary data symbol. Forexample, the generated variation may be a variation in the peakamplitude of the EMI reduction signal. At 604, the encoder varies acharacteristic of the EMI reduction signal based on the generated EMIreduction signal variation to encode the ancillary data symbol in thevaried EMI reduction signal. For example, a given ancillary data symbolcauses encoder to vary the EMI reduction signal such that the signal hasa maximum peak of 200 ppm and a minimum peak of −200 ppm. In anembodiment, the EMI reduction signal is an SSC-compliant symbol rateoffset profile (SSC profile), and the EMI reduction signal variation isa variation of the SSC profile.

FIG. 7 is a flowchart of a method 700 to decode ancillary data accordingto an embodiment of the present disclosure. At 701, the decoder receivesan EMI-reduced message signal transmitted with an EMI reduction signal,the EMI reduction signal having an EMI reduction signal variationencoding an ancillary data symbol. At 702, the decoder extracts the EMIreduction signal variation at a demodulator. At 703, the decoder decodesthe ancillary data symbol from the extracted EMI reduction signalvariation. In an embodiment, the EMI reduction signal is anSSC-compliant symbol rate offset profile (SSC profile), and the EMIreduction signal variation is a variation of the SSC profile.

The transmission of ancillary information through the SSC profilemodulator 503 can take a plurality of forms: amplitude modulation,instantaneous symbol duration modulation, or a combination of both. Therate of change of the symbol rate (i.e., the slope of the SSC profile)can also be used. Furthermore, since the SSC profile is defined over arelatively long duration (i.e., modulation at a low frequency, in therange of a few 10's of kHz), the overall shape of the SSC profile can beused to carry information, because decoding can be performed with masksor complex algorithms. Error correction codes and similar techniques canbe used to extend the bandwidth of the ancillary data transmission andimprove noise immunity. Limitations on the type of modulation mayhowever be imposed by constraints from the high-speed protocol regardingSSC profile characteristics and clock recovery performance.

FIG. 8 is a graph describing an embodiment of the present disclosurewherein the ancillary information is encoded as a modulation of theamplitude of the SSC profile variation. Both the positive and negativeexcursions of the SSC profile 800 are of equal magnitude; that is, themaximum peak 801 value is equal to the absolute value of the minimumpeak value 802. However the maximum peak 806 of the next SSC profilevariation may not be equal to maximum peak 801; similarly, the minimumpeak 807 of the next SSC profile variation may not be equal to minimumpeak 802. The SSC profile variation has a duration 804 that is constantfrom one SSC profile variation to the next. This encoding methodadvantageously removes any constant symbol rate offset between thetransmitter and the receiver. If a symbol rate offset exists between thereference symbol rate of a transmitter and that of the receiver, it willequally affect both the minimum and the maximum excursions demodulatedby the receiver. By using the difference between the maximum and theminimum excursions of the extracted SSC profile variation as the firstdecoding step, any constant symbol rate offset between the transmitterand the receiver's reference symbol rate will be removed.

In a further embodiment, each ancillary data symbol is delineated wherethe instantaneous symbol rate offset of the SSC profile crosses anominal symbol rate axis 805 with a specified slope polarity. In theexample of FIG. 8, the SSC profile from 0 ms to 30 ms shows a first SSCprofile variation representing a first ancillary data symbol, and theSSC profile from 30 ms to 60 ms shows a second SSC profile variationrepresenting a second ancillary data symbol. At the 30 ms point, theinstantaneous symbol rate offset crosses the nominal symbol rate axis805 with a positive slope, indicating the transition from the firstancillary data symbol to the second ancillary data symbol.

FIG. 9 is a graph describing an embodiment of the present disclosurewherein the ancillary information is encoded as a variation of cycleduration of the SSC profile. This encoding method can be detected at thereceiver by monitoring the time between two events of the SSC profile900. In a further embodiment, the encoding relates to the time betweeninstants 905 where the SSC profile variation crosses the nominal symbolrate axis.

In another embodiment, the encoding relates to the time between theinstants at which the SSC profile variation reaches a maximum peak 901and the time at which it reaches a minimum peak 902, or vice versa.According to this embodiment, measuring the duration of the SSC profilevariation using maximum and minimum peak values as references canprovide immunity to constant message symbol rate offset between thereceiver and the transmitter. In a further embodiment, the duration ofthe SSC profile variation is extracted by measuring the time differencebetween the maximum and the minimum peaks of the SSC profile variation,when the symbol rate changes after the minimum peak and before themaximum peak. In another further embodiment, the duration of the SSCprofile variation is extracted by measuring the time difference betweenthe minimum and the maximum peaks of the SSC profile, when the symbolrate changes after the maximum peak and before the minimum peak.

The detection of SSC profile variation peak values (maximum and minimum)can be affected by noise or slow variations of the measured SSC profilevariation in these areas. In addition to affecting decoding theamplitude of the SSC profile variation, peak detection noise can alsoaffect decoding the cycle duration of the SSC profile variation. In thecycle duration detection method above, comprising measuring the timebetween a maximum peak and a minimum peak, the noise associated withpeak detection will cause ambiguity in the detection of the cycleduration. Therefore, in a further embodiment, the cycle duration of theSSC profile variation is determined by measuring the time between pointswhen the SSC profile variation crosses a reference threshold with acertain (positive or negative) slope. For example, the cycle durationmay be determined by detecting a first time when the SSC profilevariation magnitude crosses the nominal zero axis from the negative halfto the positive half, detecting a second time when the SSC profilevariation magnitude crosses the nominal zero axis from the negative halfto the positive half, and measuring the time between the first andsecond detections. In another method, the SSC profile variation isfiltered by a low-pass filter to remove high-frequency noise. Thesemethods for determining the cycle duration of an SSC profile variationare applicable to encoding methods disclosed herein that rely on avariation of the cycle duration of an SSC profile.

In the various embodiments of FIG. 9, although the allowed range of theduration of the SSC profile variation may be relatively narrow, its lowfrequency nature (10's of kHz) can lead to a large number of quantizedlevels that can be detected precisely, and thus lead to a significantcontribution to the number of ancillary data bits that can be encoded ineach SSC profile variation.

FIG. 10 is a graph describing an embodiment of the present disclosurewherein the encoding schemes described in FIG. 8 and FIG. 9 are combinedto produce a two-dimensional constellation. This encoding method retainsthe immunity to constant symbol rate offsets from the method describedin FIG. 8. When no constant symbol rate offset between the transmitterand the receiver exists, both maximum and minimum peak values of the SSCprofile variation extracted by the receiver are expected to be of equalmagnitude. When a symbol rate offset exists between the transmitter andreceiver, the constant symbol rate offset between the receiver and thetransmitter can be measured by averaging the maximum and the minimumpeak values of the extracted SSC profile variation, preferably over alarge number of SSC profile variation cycles.

FIG. 11 is a graph showing that this extracted average symbol rateoffset can be used as the threshold for a trigger to measure timeinstants to compute the duration of the SSC profile variation, reducingthe error of the transmitted ancillary data. Assuming that the samereference clock is used on the transmitter side both to generate thenominal message symbol rate and to generate the instantaneous symbolrate specified by SSC profile variation 1101, the extracted SSC profilevariation 1102 duration will scale according to the extracted averagemessage symbol rate offset 1103. Therefore, according to the presentembodiment, the extracted SSC profile variation duration is adjustedaccording to the measured constant symbol rate offset between thetransmitter and the receiver.

A further embodiment method can change the encoding according to theerror rate received. The number of SSC profile variation amplitudelevels, the number of SSC profile variation duration levels, and whetherone or two ancillary data symbols are sent per SSC profile variation canbe adjusted to provide a target error rate of the ancillary data.

FIG. 12 is a graph describing an embodiment of the present disclosurewherein the ancillary information is encoded as a modulation of the SSCprofile variation minimum peak value 1201 only, while keeping themaximum peak value constant. The exemplary SSC profile of FIG. 12 havingonly a downspread modulation is compliant with SSC modulation protocolsthat require a fixed maximum value.

FIG. 13 is a graph describing an embodiment of the present disclosurewherein the encoding schemes described in FIG. 9 and FIG. 12 arecombined to produce a two-dimensional constellation. The embodiments ofFIG. 12 and FIG. 13 are similar to the embodiments of FIG. 8 and FIG.10, respectively, but are adapted for cases where the SSC profile isconstrained to have a fixed maximum or minimum peak value. In theembodiments of FIG. 12 and FIG. 13, it is not possible to use thenominal symbol rate offset crossing of the SSC profile variation, or touse the SSC profile variation average offset, to measure the cycleduration of the SSC profile variation. However, the modulation of only aminimum or maximum SSC profile symbol peak value will still allow forthe same encoding methods discussed previously.

FIG. 14 is a graph describing an embodiment of the present disclosurewherein the ancillary information is encoded as a modulation of the SSCprofile variation peak values. The peak value may be a maximum 1402 or aminimum 1401, but unlike the embodiments of FIG. 12 and FIG. 13, theembodiment of FIG. 14 is not constrained to a constant maximum value ora constant minimum value. The cycle duration of each SSC profilevariation is constant; therefore, each ancillary data symbol has thesame duration.

FIG. 15 is a graph describing an embodiment of the present disclosurewherein the SSC profile provides three degrees of freedom, allowing moreancillary data bits to be encoded in each SSC profile variation. Theancillary data is encoded as the modulation of the cycle duration of theSSC profile variation, and as modulation of both a maximum peak valueand minimum peak value of the SSC profile symbol values, the modulationof the duration, the modulation of the maximum peak, and the modulationof the minimum peak values each being independent. The exemplary SSCprofile of FIG. 15 shows two separate SSC profile variations,representing two ancillary data symbols. The first SSC profile variationis demonstrated by a first maximum peak (1000 ppm), a first minimum peak(−1500 ppm) and a first cycle duration (27 ms); the second SSC profilevariation is demonstrated by a second maximum peak (1300 ppm), a secondminimum peak (−700 ppm) and a second cycle duration (33 ms).

The extraction of the constant symbol rate offset between thetransmitter and the receiver is more difficult because the receivedsignal cannot be averaged to determine a constant symbol rate offsetbetween the expected symbol rate and the received symbol rate. Thisconstant symbol rate offset is necessary to reduce the error rate at thereceiver according to the embodiment of FIG. 11. Therefore, in otherexemplary implementations of the embodiments of FIG. 14 and FIG. 15,pilot symbols are sent at predefined instants. These pilot symbols havedefined characteristics that allow the receiver to compute any variationso as to compensate the measured characteristics of the SSC profilevariations received afterward. For example, the difference between theextracted maximum value of the SSC profile symbol and the expectedmaximum value can be used to compute the constant symbol rate offsetbetween the receiver and the transmitter.

Those skilled in the art will recognize that many variants exist forsending pilot symbols, for example sending them at link initialization,periodically, after a predefined pattern, upon request by the far-end,or by a combination of methods. The number of different pilot symbolssent for addressing different characteristics of the signal and therepetition of pilot symbols to reduce errors in their detection throughaveraging are design trade-offs to take into account, as theyeffectively reduce the ancillary data bit rate, at the benefit ofimproved reliability.

Pilot symbols can also carry some payload information, for example bymodulating the duration of the SSC profile variation, while forcing themaximum and minimum values of the SSC profile variation to have equalbut opposite magnitudes, as described in the embodiment of FIG. 9. Thisallows extraction of the constant symbol rate offset, while stillcarrying ancillary information encoded in the variation of the durationof the SSC profile. Therefore, in an embodiment, the pilot symbol usedin the SSC transmission method of FIG. 14 or FIG. 15 is the SSCmodulated signal in the embodiment of FIG. 9.

Pilot symbols can be used to calibrate the extracted SSC profile symbolduration for any of the embodiments of FIG. 9, 10, 13, 15 or 16.

The embodiments of FIG. 12 and FIG. 14 can modulate the transmittersymbol rate such that its average will not be zero, and this averagevalue may vary according to the transmitted SSC profile variation. Thoseskilled in the art will recognize that this situation may requireperiodic bit insertion or bit removal, and care must be taken not toexceed specified limits of the message transmission protocol used. Somecoding schemes transmit compensation bits or symbols to ensure that theaverage symbol rate offset introduced by the SSC modulation is keptwithin acceptable limits.

FIG. 16 is a graph describing an embodiment of the present disclosurewherein the ancillary information is encoded in both the modulation ofthe amplitude and modulation of the duration of the SSC profilevariation 1600. In this embodiment, the SSC profile variation 1600duration is detected by the receiver at zero crossings 1602 of the SSCprofile variation amplitude with the nominal symbol rate axis. Theancillary information is further encoded as a modulation of either theSSC profile variation minimum peak 1603 or maximum peak 1604, similarlyto the embodiment of FIG. 14.

In the operation of an embodiment communications system, the SSCprofiles of the various foregoing embodiments can be achieved withminimal or no modification over known communications systems. Thus, mostcurrent communications systems can be adapted to provide bothSSC-compliant peak EMI reduction and carry ancillary data in ahigh-speed channel without separate channel filters.

Referring back to FIG. 5, the transmitter does not require anyadditional circuitry. The SSC modulator only needs to be modified toaccept the encoded SSC profile variation described in the variousembodiments of the present disclosure. The SSC modulator 503 istypically a relatively low-speed digital circuit, so adding supplementallogic can be performed at a low cost to both power and complexity. TheSSC profile encoder 502 is also implemented as a relatively low-speeddigital circuit.

Those skilled in the art will recognize that both the SSC modulator 503and the SSC profile encoder 502 circuits can be realized in a number ofways, particularly through RTL code synthesis or even using computerprograms.

Receivers that support SSC typically have a type-II feedback loop. Thoseskilled in the art will recognize that this type of feedback looptypically contains a frequency tracking circuit, which tracks thehigh-speed baud rate offset of the received signal with respect to aninternal reference. This circuit thus provides a signal proportional tothe SSC profile and the SSC profile variation, as extracted from theincoming high-speed signal. This SSC profile variation is decoded byadditional decoding circuits. Decoding is a relatively low-speed processthat can be realized through digital synthesis or computer programs.

FIG. 17 is a block diagram of a receiver 1700 according to an embodimentof the present disclosure. Receiver 1700 comprises a type-II clockrecovery loop 1701. The output of integrator 1702 is extracted as asignal proportional to the SSC profile variation. In a furtherembodiment, a scaling factor is used to modify the amplitude to get theextracted SSC profile variation; in a different embodiment, no scalingfactor is used and the decision thresholds or masks are scaled by theinverse proportion of the scaling factor. The output of integrator 1702can thus be considered as the extracted SSC profile variation.

Receiver further comprises a positive peak detector 1711 circuit todetect the time at which the extracted SSC profile variation reaches amaximum peak amplitude, and to also detect the amplitude. This is doneby comparing the current SSC profile variation with previous values andretaining the largest value and its corresponding instant from aninternal time base. Those skilled in the art will recognize that thisdetection can be performed in a number of ways. In an embodiment, thepeak detection method includes: (a) sending a strobe signal to theprocessor when a larger value is found, the processor recording theinternal time; (b) detecting from samples of the SSC profile variation,or working from a digitized SSC profile variation; (c) filtering the SSCprofile variation before detecting its maximum value to remove noise;and (d) resetting the detector after a given amount of time, for examplehalf the expected average SSC profile variation duration, to be ready tocapture the next cycle's maximum value.

Negative peak detector 1712 circuit functions similarly to the positivepeak detector circuit, but detects the minimum amplitude and itsoccurrence instant.

Comparator 1713 circuit compares the SSC profile variation with athreshold value set by the processing unit 1704, and outputs a signalindicating that the SSC profile variation is larger than this threshold.

Processing unit 1714 collects the information from the above circuitsand implements the demodulation of the SCC profile variation.

Receiver 1700 is similar to a conventional SSC-compliant receiver inthat receiver 1700 includes a type-II clock recovery circuit 1701;however, receiver 1700 can further decode ancillary data transmittedaccording to an embodiment of the present disclosure by augmenting clockrecovery circuit 1701 with a positive peak detector 1711, a negativepeak detector 1712, a comparator 1713, and a processing unit 1714. Thus,with the addition of the foregoing circuits, a conventionalSSC-compliant receiver can be designed to decode ancillary datatransmitted in the method of the present disclosure.

In an exemplary embodiment, an SSC profile is chosen to have 4 amplitudelevels and 8 SSC profile variation durations. Thus, the ancillary datais grouped in sets of 32 symbols that are each mapped to one uniquecombination (i.e. symbol) of the SSC amplitude levels and SSC variationduration. The selected SSC profile variation is then used to modulatethe reference clock to transmit the message over the communicationsystem of FIG. 5.

FIG. 18 is a flowchart of method 1800, which is performed by receiver ofFIG. 17 after it receives the SSC profile variation. At 1801, processingunit sets the average symbol rate offset signal to zero. At 1802,processing unit sets a correction factor to 1. At 1803, processing unitwaits for a rising edge of the comparator. At 1804, processing unitrecords the time. At 1805, processing unit computes the differencebetween the maximum and minimum SSC profile variation peak amplitudesdetected within the same SSC profile variation, i.e. between two risingedges of the comparator. At 1806, processing unit computes the sum ofthe maximum and minimum SSC profile variation amplitudes detected withinthe same SSC profile variation. At 1807, processing unit resets themaximum and minimum peak detectors. At 1808, processing unit computesthe difference between the current time of the rising edge of thecomparator with the time recorded from the previous rising edge to getthe SSC profile variation duration. At 1809, processing unit computesthe correction factor for the SSC profile variation duration as theopposite of half the sum of the maximum and minimum SSC profilevariation peak amplitudes, with the appropriate unit scaling. At 1810,processing unit scales the SSC profile variation duration by thecorrection factor. At 1811, processing unit maps the SSC profilevariation duration and peak-to-peak amplitude to their closest definedencoding level, and decodes the ancillary data from the correspondingset of ancillary data symbols. At 1812, processing unit sets thecomparator threshold to half the sum of the maximum and minimum SSCprofile variation peak amplitudes. This concludes a first processingunit cycle and processing unit loops back to 1803.

The preceding embodiments describe methods of encoding and decoding theancillary data within any generic SSC profile The transmitter and thereceiver shown in FIG. 5 is configured to perform the methods ofencoding and decoding described above for the particular SSC profilechosen. The necessary configuration and components of the transmitterand receiver for a chosen SSC profile would be known to a person ofskill in the art.

For example, in an embodiment, a low-pass filter before peak detectorsand comparator aids in removing noise in the receiver.

In an embodiment of the present disclosure, the processing unit receivesdirectly, or after filtering, the SSC profile variation, and compares itto a mask. In another embodiment, processing unit performs the peakdetection and comparison. In another embodiment, processing unitperforms other decoding functions based on the SSC profile variationcharacteristics. The relevant characteristics of an SSC profilevariation characteristics can include, peak maximum and minimum values,slope, and duration

In the embodiments of the present disclosure, the transition density ofthe received data stream directly affects the ratio between thefrequency tracking accumulator and the modulated symbol rate of theinput signal since the phase error detector outputs a null value when notransition is present. This problem can be compensated by scaling thephase error signal by a number that represents the number of consecutiveidentical symbols transmitted before the current transition. The averagetransition density can also be computed and used for scaling, in case itis assumed constant. In systems where multiple symbols are processedtogether in a set to generate a combined phase error signal representingthe sum of the phase error signal for all symbols in the set, thiscompensation scaling can represent the average number of consecutiveidentical symbols before each of the transitions contained in the set.

In a further embodiment of the present disclosure, communications system500 is a duplex communications system. A controller on each transmit andreceive side of the duplex communications system evaluates the qualityof the ancillary data signal received through the high-speed signaltransmitted according to the spread-spectrum clocking methods of thepresent disclosure. The controller then determines whether the symbolrate should be increased, decreased, or maintained. This determinationcan be made, for example, by comparing the quality of the receivedancillary data signal against thresholds of a pre-determined metric. Thecontroller at the receiver side of the duplex communications system cansend specific instructions to the transmitter using a duplex link torequest increments or decrements in the symbol rate.

In the preceding description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe embodiments. However, it will be apparent to one skilled in the artthat these specific details are not required. In other instances,well-known electrical structures and circuits are shown in block diagramform in order not to obscure the understanding. For example, specificdetails are not provided as to whether the embodiments described hereinare implemented as a software routine, hardware circuit, firmware, or acombination thereof.

Embodiments of the disclosure can be represented as a hardware productimplemented in an Integrated Circuit (IC), Programmable Gate Array, orsome combination of Integrated Circuit(s), Programmable Gate Array(s),and Software. Those of ordinary skill in the art will appreciate thatother functions can also be implemented on such Integrated Circuits orProgrammable Gate Arrays.

The above-described embodiments are intended to be examples only.Alterations, modifications and variations can be effected to theparticular embodiments by those of skill in the art without departingfrom the scope, which is defined solely by the claims appended hereto.

What is claimed is:
 1. A method for decoding ancillary information at areceiver in a high-speed communications network, the method comprising:receiving an EMI-reduced message signal transmitted with aspread-spectrum clocking (SSC) profile, the SSC profile having an SSCprofile variation encoding an ancillary data symbol; extracting the SSCprofile variation at a demodulator; receiving a pilot symbol; correctingthe extracted SSC profile variation according to the pilot symbol; anddecoding the ancillary data symbol from the extracted SSC profilevariation at a decoder, including comparing a peak-to-peak amplitude ofthe SSC profile variation to an expected peak-to-peak amplitudecorresponding to the ancillary data symbol, wherein decoding comprisescomparing a peak-to-peak amplitude of the SSC profile variation to anexpected peak-to-peak amplitude corresponding to the ancillary datasymbol.
 2. The method of claim 1, wherein decoding comprises comparingthe SSC profile variation to a mask corresponding to the ancillary datasymbol.
 3. The method of claim 1, further comprising: correcting theextracted SSC profile variation by the difference between the magnitudeof the maximum peak and the magnitude of the minimum peak of theextracted SSC profile variation, the expected magnitude of the maximumpeak equal to the expected magnitude of the minimum peak.
 4. The methodof claim 1, further comprising: correcting the extracted SSC profilevariation by the average magnitude of the extracted SSC profilevariation, the expected average magnitude equal to zero.
 5. The methodof claim 1, wherein the SSC profile has a constant cycle duration, andthe SSC profile comprises a plurality of sections, the sum of thedurations of all the SSC profile sections being equal to the constantcycle duration of the SSC profile.
 6. A method for decoding ancillaryinformation at a receiver in a high-speed communications network, themethod comprising: receiving an EMI-reduced message signal transmittedwith a spread-spectrum clocking (SSC) profile, the SSC profile having anSSC profile variation encoding an ancillary data symbol; extracting theSSC profile variation at a demodulator; decoding the ancillary datasymbol from the extracted SSC profile variation at a decoder, includingcomparing a peak-to-peak amplitude of the SSC profile variation to anexpected peak-to-peak amplitude corresponding to the ancillary datasymbol, wherein decoding comprises comparing a peak-to-peak amplitude ofthe SSC profile variation to an expected peak-to-peak amplitudecorresponding to the ancillary data symbol; selecting an EMI reductionsignal variation bin corresponding to the extracted EMI reduction signalvariation, the EMI reduction signal bin being a nominal value mapped toa range of EMI reduction signal variation values; and decoding, at adecoder, the ancillary data symbol from the selected EMI reductionsignal variation bin.
 7. The method of claim 6, wherein the range of EMIreductions signal variation values is at least twice the expectedmaximum constant difference between a received symbol rate and atransmitted symbol rate.
 8. A receiver for decoding ancillaryinformation in a high-speed communications network, the receivercomprising: an input configured to receive an EMI-reduced message signaltransmitted with a spread-spectrum clocking (SSC) profile, the SSCprofile having an SSC profile variation encoding an ancillary datasymbol; a demodulator configured to extract the SSC profile variation,receive a pilot symbol, and correct the extracted SSC profile variationaccording to the pilot symbol; and a decoder for decoding the ancillarydata symbol from the SSC profile variation, including comparing apeak-to-peak amplitude of the SSC profile variation to an expectedpeak-to-peak amplitude corresponding to the ancillary data symbol,wherein decoding comprises comparing a peak-to-peak amplitude of the SSCprofile variation to an expected peak-to-peak amplitude corresponding tothe ancillary data symbol.